Nuclear medicine imaging

Nuclear medicine is a branch of medical imaging that uses radiopharmaceuticals to examine the function and structure of organs and tissue function and structure.

A radiopharmaceutical is generally made up of 2 parts: a pharmaceutical that targets a specific organ or tissue and a radioactive material (radionuclide) that gives off small amounts of radiation.

A small amount of radiopharmaceutical is injected, swallowed or inhaled into the body. The pharmaceutical part acts like a chemical that the body normally uses, so the body tissues “take up” the radiopharmaceutical. The radioactive part gives off radiation (gamma rays) that is detected by a special device. The device used depends on the organ or tissue being studied. It may be a gamma camera or a positron emission tomography (PET) scanner or probe. These devices record the gamma rays given off, and then a computer uses this data to make an image.

Nuclear medicine images can be used to find tumours in 2 ways:

The tumour concentrates, or “takes up,” more of the radiopharmaceutical than the rest of the organ or tissue.

The rest of the organ or tissue concentrates, or “takes up,” the radiopharmaceutical, but the tumour doesn’t.

There are 4 different types of nuclear medicine images:

dynamic – a series of images that captures movement or activity (such as blood flow to an organ)

planar (static) – a 2-dimensional view that shows one image at a time

whole body – front and back views of the body in 2 dimensions

single photon emission computed tomography (SPECT) – a 3-dimensional view of the process or function of the organ being studied

Different radioactive isotopes are used depending on the type of test and the tissue or organ being studied, including:

technetium-99m (Tc-99m)

radioactive iodine

strontium

gallium

thallium

In some centres, nuclear medicine images can be superimposed with computed tomography (CT) or magnetic resonance imaging (MRI). Newer devices available in some centres may be able to perform 2 imaging studies at the same time, such as SPECT/CT and PET/CT.

Why nuclear medicine imaging is done

check the structure and function of tissues or organs, such as the brain, thyroid, lungs, heart, liver, spleen, kidney and bone

detect disease in organs or bones

find tumours, especially in the bones and thyroid

determine the stage (how far cancer has spread and if it is present in other organs and tissues)

find out if cancer treatment is working

How nuclear medicine imaging is done

Tests are usually done as an outpatient procedure in the nuclear medicine department of a hospital. Scanning takes from 15 minutes to a few hours, depending on the part of the body being scanned. For some tests, the person must return hours or days later for another series of scans.

No special preparation is needed for most nuclear medicine imaging tests. Some tests may require fasting for 2–12 hours before the test.

Before the scan, the doctor will take a history of previous surgery, cancer therapy, allergies or sensitivity to any substances or drugs, current symptoms and physical findings. It is important for women to tell the nuclear medicine staff if they are breast-feeding, pregnant or think they may be pregnant.

The radiopharmaceutical is given before the scan.

The radiopharmaceutical may be:

injected into a vein in the hand or arm (most common)

given by mouth (orally)

inhaled

It may take a few minutes or a few hours for the radiopharmaceutical to collect in the organ or tissue. When the radiopharmaceutical has collected in the organ or tissue, the scan will begin.

During the nuclear medicine scan:

The person sits or lies down on a special table.

If lying on the back for long periods of time causes discomfort, the person may be given a pain reliever before the test.

The person is asked to stay very still during imaging, as movement may distort the images.

Velcro straps are fastened around the person to hold them safely and help them lie still.

The person may be asked to change position so that images can be taken from different angles.

Most nuclear medicine procedures are performed using a gamma camera.

There are several types of gamma cameras:

stationary cameras

cameras that move across the body

cameras that rotate around the body (SPECT)

The gamma camera may be:

dual-headed, with one camera above and one below the table

within a large, doughnut-shaped scanner similar to a CT or MRI unit

beneath the table, out of view

Other devices that may be used include a PET scanner or probe.

A PET scanner is a large machine with a round doughnut-shaped hole in the middle, similar to a CT or MRI unit.

A probe is a small hand-held device that detects and measures the radiopharmaceutical in the body.

The gamma camera or PET scanner or probe is positioned a few inches over the person’s body. It picks up the pattern of radioactivity given off by the radiopharmaceutical.

A computer analyzes the patterns and creates 2- or 3-dimensional images (sometimes with colour).

A nuclear medicine doctor views and interprets the images.

After the scan, the radioactive material quickly loses its radioactivity. It passes out of the body through the urine or stool (feces). Depending on the type of radiopharmaceutical used, it may take a few hours or days to completely pass out of the body.

Drinking fluids after the procedure helps flush the radiopharmaceutical from the body.

Instructions may be given for special precautions that need to be taken after urinating, such as to flush the toilet twice and to wash the hands thoroughly.

Potential side effects

The dose of x-rays or radioactive materials used in nuclear medicine imaging can vary widely. Dose depends on the type of procedure and body part being examined. In general, the dose of radiopharmaceutical given is small and people are exposed to low levels of radiation during the test. The potential health risks from radiation exposure are low compared with the potential benefits. There are no known long-term adverse effects from such low-dose exposure.

Some potential side effects that might occur include:

Bleeding, soreness or swelling may develop at the injection site.

Allergic reactions to the radiopharmaceutical may occur, but are extremely rare.

What the results mean

Radiopharmaceuticals are absorbed differently by different body tissues, which will help the doctor interpret the nuclear medicine images.

Abnormal areas in an organ absorb different amounts of the radiopharmaceutical.

Cancerous tissue may absorb more or less of the radiopharmaceutical than normal tissue.

Other diseases, such as arthritis, can also affect absorption (uptake) of the radiopharmaceutical.

What happens if a change or abnormality is found

The doctor will decide whether further tests, procedures, follow-up care or additional treatment are needed.

Special considerations for children

Being prepared for a test or procedure can reduce anxiety, increase cooperation and help the child develop coping skills. Parents or caregivers can help prepare children by explaining to them what will happen, including what they will see, feel and hear during the test.

Sometimes special preparation is needed for nuclear medicine imaging.

Children may need to fast for 2–12 hours before the test if the stomach is being examined.

Children will be asked to drink plenty of water before a scan of the kidneys.

A catheter may be placed for some bladder exams.

Tell children that they may feel some discomfort when the catheter is inserted.

Most studies involve an intravenous injection of the radioactive isotope.

A cream may be used to numb the area.

Explain to children that they will feel:

a sharp prick when the needle is inserted

slight pressure or tugging when the radioactive isotope is injected

Children need to lie still on the exam table during the scan, which may be unpleasant for them.

Bring a bottle of juice, milk or formula to help the child relax and fall asleep during the scan.

Some children may like to hold a special toy or blanket during the scan.

Children could listen to music or a story during the scan.

The parent or caregiver can stay with the child and help them lie very still.

Pregnant women cannot stay in the room during the scan.

The dose of radioactive material is based on the weight of the child, and the least possible dose is given. The small amount of radioactive material given to the child should not cause any concerns. Nuclear medicine has been used in newborns and children for more than 30 years and there are no known long-term adverse effects from such low-dose studies.

Instructions may be given for special precautions that need to be taking when caring for children during the first 6–24 hours after the test:

If the caregiver is pregnant, someone else should do most of the child care.